The digital communication system where multiple users irregularly transmit data (hereinafter referred to as a “discontinuous digital communication system) uses an auto gain control method similar to that of a digital communication system where a single user transmits a continuous data packet (hereinafter referred to as a “continuous digital communication system”). That is, based on a signal envelope or the average energy, an AGC gain value is determined in inverse proportion to the average.
A method for controlling the AGC gain value with the average is suitable for a continuous digital communication system, but is not suitable for a discontinuous digital communication system.
The reason is because a continuous digital communication system continuously receives data uninterrupted once communication is begun, while the discontinuous digital communication system does not uninterruptedly and continuously receive data or experiences a sudden change in signal energy. That is, when data are suddenly received after a period of data reception dormancy, or received signal energy suddenly changes, AGC is not performed well. In other words, since the auto gain control method has a large gain value for scaling a narrow region for a certain duration, data (which are suddenly received or change in signal energy) overrun the current scale region.
Accordingly, when the data signal is converted into a digital signal by an analog-to-digital converter, the maximum saturation value occurs or bit resolution decreases, causing a great amount of distortion.